Distributor for micro-quantities of liquid

ABSTRACT

An ultra low flow liquid distributor generates a very thin yet continuous liquid film over the entire width of a transfer surface. The ultra low flow liquid distributor includes a liquid supply system starting from a common main supply, which is split by repetitive bifurcations into a multitude of liquid sub-mains, until eventually each liquid supply sub-main feeds into one of the many liquid outlet openings. In this the liquid outlet openings are arranged above the liquid supply system, which automatically ensures self-priming.

[0001] This invention concerns an ultra low flow liquid distributor togenerate a thin film of liquid on a surface, which is to be moistened.

[0002] When dispersing liquids on transfer surfaces of gas/liquidcontact reactors, e.g. of plate transfer reactors, the liquids areusually sprinkled or sprayed on using appropriate devices (sprinklers,nozzles, jets, droplet distributors, etc.)

[0003] Devices with open or closed trays or ducts in connection withoverflows and/or liquid outlet openings are used as well.

[0004] For example, from DE-OS 43 21 743 a liquid distribution device isknown, with which a liquid is dripped onto a non-woven fabric from aporous tube. Also known from this document is the use of spraydistribution devices.

[0005] From DE 36 40 886 C1 a liquid distributor for mass and heattransfer columns is known, which consists of one main distributiondevice with parallel ducts in the form of trays, in which the sidewallsof the trays are perforated to release the liquid. In longitudinaldirection along the outside of the walls of the channels, guiding metalfins are affixed, which on the one hand encompass the perforations withrecesses from below and thus exercise a centering effect on the liquidThis has a centering effect on the liquid flowing down the sidewalls ofthe trays while the guiding fins on the other hand have cut-outs thatare downward offset to the recesses and which guide the liquid todripping tongues lying in between.

[0006] With these conventional liquid distributors the risk of dropletformation arises and with that the associated risk of small dropletsbeing carried out by the gas flow and consequently their discharge outof the reactor. Therefore these conventional liquid distributors requiredemisters downstream in the gas flow, which cause additional cost.

[0007] To distribute very small amounts of liquid so-called thin filmevaporators or thin film absorbers are known, in which a mechanicalwiper disperses a thin film of liquid onto a transfer surface. Thisdesign requires considerable effort with regard to construction,involves numerous moving parts and is therefore expensive, prone tomalfunction and requires high maintenance.

[0008] Designs with open or closed trays or ducts in connection withoverflows and/or outlet openings bear the risk of silting up andclogging, respectively. In the particular application as airdehumidifiers (absorbers) for air conditioning systems it was to thisdate not economically feasible, to disperse the physically requiredlowest possible mass flow of liquid (adsorbent, usually a concentratedsalt solution), which is required for the absorption of water vapourfrom the air, in such a way onto the mass transfer surfaces of anappropriate reactor, that an extremely thin, yet continuous film ofliquid could cause a significant concentration change in the liquid(sorbent).

[0009] Therefore it is the task of the invention described herein tooutline an ultra low flow liquid distributor for minimum amounts ofliquids which generates a thinnest possible liquid film across theentire width of a transfer surface. Furthermore it is the task of thisinvention, to outline a mass- and heat transfer reactor with such anultra low flow liquid distributor.

[0010] The solution of these tasks is fulfilled with the characteristicsin accordance with Claim 1 and 11, respectively.

[0011] The specially shaped duct system, which is formed by thebisection at the bifurcations and the regularly arranged outletopenings, allows the dispersion of minimum amounts of liquid evenlywithout any supporting mechanical device, with regard to location aswell quantity. By arranging the outlet openings above the liquid supplysub-mains; gas bubbles can easily escape, in particular during the startup of the ultra low flow liquid distributor. With the ultra low flowliquid distributor in accordance with this invention, mass transferreactors can be built, in which extremely little liquid (sorbent) isused on a large, moistened mass transfer surface, so that the ratiobetween gas mass flow and liquid mass flow can be >50. The ultra lowflow liquid distributor in accordance with this invention can beinstalled directly on the surface, which is to be moistened, so thatfree droplets cannot form. An additional demister is therefore notrequired.

[0012] In accordance with an advantageous design of this invention inaccordance with Claim 2 the outlet openings are arranged in equaldistance along the surface, which is to be moistened. This results inthe even distribution of the liquid and establishes a homogenous andcontinuous thin liquid film.

[0013] In accordance with an advantageous design, the ducting isdesigned in such way that the fluid-flow in the liquid supply sub-mainsis directed from bottom to top, against the gravity. This effects aself-priming of the liquid supply system during operation and duringre-start after starvation of the distributor. This prevents thedisturbance of the liquid flow by gas bubbles in the liquid supplysub-mains and consequently the disturbance of the even distribution inthe ducts (Claim 3).

[0014] In accordance with an advantageous design of the invention inaccordance with to Claim 4 the liquid flow is split in two equal partsat each bisection and the total length of each liquid supply sub-mainfrom the main liquid supply to the respective liquid outlet opening isequal. This ensures the maximum possible total running length for eachfluid particle and consequently the maximum possible pressure differencebetween the liquid supply main inlet and the liquid outlet opening.

[0015] A malfunctioning of the liquid distributor due to pressurefluctuations during operation or clogging due to dust particles in areasof low or negligible flow rates is prevented due to the rounded designof the ducts at the bifurcations, following the flow direction (Claim5).

[0016] The ultra low flow liquid distributor in accordance with thisinvention consists of a base body with a front and a rear side. The basebody has a certain thickness and length, which match the mass transferplate to be moistened. This prevents a disturbance of the gas flow,which is passing the transfer surface. In this base body, a liquidsupply system is integrated in such a way, that it branches further andfurther towards the liquid outlet openings, starting at a common liquidsupply main. The liquid, which enters the ultra low flow liquiddistributor in accordance with this invention, either continuously orintermittently, is split at each bifurcation into two mass flows ofequal size when flowing through this liquid distributor (Claim 7).

[0017] In accordance with an advantageous design of this invention inaccordance with Claim 8 two transfer surfaces can be moistenedsimultaneously with this ultra low flow liquid distributor

[0018] In accordance with a preferred design of this invention theliquid outlet openings are arranged in a straight line. This supportsthe generation of an even liquid film. (Claim 9).

[0019] The formation of droplets when the liquid is discharged at theoutlet openings can be prevented by an advantageous design of theinvention, where the outlet openings are shaped tapered, with the wideropening pointing outwards in accordance with Claim 10.

[0020] A mass and heat transfer reactor with such an ultra low flowliquid distributor (Claim 11) is almost maintenance free and allows thegeneration of a very thin and homogenous sorbent film on the mass- andheat transfer surfaces.

[0021] The remaining sub claims refer to further advantageous designs ofthe invention.

[0022] Regarding the design of the coating on the mass-and heat transfersurfaces, reference is made to the patent application with the title“Mass and Heat Transfer Surface” which was submitted on the same day,Reference No. P/11ZA0722/DE, in its entirety.

[0023] With regard to the design of the mass and heat transfer reactor,reference is also made to the patent application with the title “Massand Heat Transfer Reactor” which was submitted on the same day,Reference No.: P/11ZA0720/DE in its entirety.

[0024] Further details, characteristics and advantages of the inventionresult from the following description of preferred designs in accordancewith the drawings.

[0025] Shown are:

[0026]FIG. 1 a schematic drawing of a typical design of the invention

[0027]FIG. 2 a schematic cross section though one of the mass and heattransfer surfaces.

[0028]FIG. 3 a front view of the liquid distributor.

[0029]FIG. 4a a detail of the rear view of the liquid distributor

[0030]FIG. 4b a cross section through FIG. 4a along line D-D;

[0031]FIG. 5a, b und c cross sections along lines A-A, B-B and C-C inFIG. 3;

[0032]FIGS. 6 and 7 an alternative design of the liquid distributor; and

[0033]FIG. 8 a detail of FIG. 3.

[0034] The typical design of the invention shown in FIG. 1 has amultitude of vertical reactor double plates 2, which are arrangedside-by-side with some space in-between. Each of the reactor doubleplates 2 has one upper end 4, one lower end 6, one first and one secondmain surface 8 and 10 respectively, and a void 12 between first andsecond main surface 8 and 10. The void 12 is shaped to form a heattransfer duct system 14, in which e.g. water can circulate as a heatingor cooling media HKM. Between the individual reactor double plates 2, amass transfer duct system 16 is formed. The first and second mainsurfaces 8 and 10 of the reactor double plates 2 are designed as massand heat transfer surfaces 18. The mass and heat transfer surfaces 18are moistened continuously from the top by a liquid medium FM or asorbent. From the bottom, in counter-flow direction, a gaseous mediumflows between the reactor double plates, which releases—in case ofabsorption—a gaseous component into the sorbent FM and absorbs the samegaseous component from the sorbent FM in case of desorption.

[0035] At the upper end 4 of the reactor double plates 2, a liquiddistributor or ultra low flow liquid distributor 20 is attached, whichprovides sorbent FM across the entire width of the reactor double plates2 on all mass and heat transfer surfaces 18 to form a thin film ofliquid. Details of the liquid distributor 20 are described in FIG. 3, 4and 5.

[0036] The mass and heat transfer surfaces 18 have a coating 21consisting of small solid particles 22, for example sand grains, asschematically shown in FIG. 2. The mass and heat transfer surfaces 18thus have a surface like sandpaper. Between the individual solidparticles or sand grains 22, respectively gaps and voids 24 are formed.These small gaps and voids 24 by their capillary effect cause the evendistribution of sorbent FM in the form of a thin liquid film 26 on themass and heat transfer surfaces 18. As shown in FIG. 2, the sand grains22 are applied individually, side-by-side on the mass and heat transfersurfaces 18. This single layer application enables the formation of avery thin film of liquid.

[0037] The coating 21 and the sand grains 22, respectively are fixedpermanently on the mass and heat transfer surface 18, using glue.Alternatively, the coating can be fixed onto an intermediate carrier,which is not shown, which itself can be fixed onto the mass and heattransfer surfaces 18.

[0038]FIG. 3 to 5 show a typical design of a liquid distributor 20,which is used to apply the liquid sorbent FM from the upper end 4 of thereactor double plates 2 onto the mass and heat transfer surfaces 18. Theliquid distributor 20 consists of a base body 27 in the form of arectangular panel with a front side 28 and a rear side 29. The width “b”and thickness “d” of the liquid distributor correspond to the width andthickness of the reactor double plates 2. Along the upper edge of theliquid distributor 20, front and rear liquid outlet openings 30 and 32are situated at regular intervals side by side, whereby the front andrear openings 30 and 32 are alternating. Therefore the front liquidoutlets 30 moisten the front side 28 of the liquid distributor 20 andthe first main surface 8 of a reactor double plate 2, while the rearliquid outlet openings 32 moisten the rear side 29 and the second mainsurface 10.

[0039] The liquid outlet openings 30 und 32 receive the liquid orsorbent FM, respectively via a liquid supply system 34. The liquidsupply system 34, which is shown on the front side 28, includes a commonmain supply 36 and a multitude of sub-mains 38. The liquid main supply36 is branched by repetitive bifurcations 40 into liquid supplysub-mains 38, until one liquid supply sub-main 38 is available for eachliquid outlet opening 30 and 32. The design as shown in FIG. 3 has 64liquid outlet openings 30 leading to the first main surface 8 and 64liquid outlet openings 32 leading to the second main surface 10. Theliquid main supply 36 branches at the first bifurcation 40 into twosub-mains 38, which are split another five times, every time into twosub mains until one individual sub main 38 is available for each of the128 liquid outlet openings 30 and 32.

[0040] The liquid main supply 36 is equipped with a connection pipe 42,which lies above the upper edge of the liquid distributor 20 and servesto feed the liquid sorbent into the system. The liquid main supply 36ends at the lowest point of the liquid supply system 34 and the liquidsupply sub-mains 38 are always directed either horizontally orvertically, pointing upwards against gravity. This arrangement of liquidsupply sub mains 38 prevents the formation of gas bubbles in the liquidsupply system 34, which could lead to a discontinuous film formation.

[0041] The details in FIG. 5a und FIG. 5c show, that the liquid supplyopenings 30 and 32 are shaped tapered, with the wider opening pointingoutwards. This shape prevents the formation of droplets when liquidsorbent FM leaves the liquid outlet openings 30 and 32 and ensures thecontinuous moistening of the mass and heat transfer surfaces 18. In thearea below the liquid outlet openings 30 and 32, both front side 28 andrear side 29 of the liquid distributor 20, are equipped with the samecoating 21 as the mass and heat transfer surfaces 18. This ensures acontinuous formation of a liquid film, starting from the liquid outletopenings 30, 32 and reaching to the lower end 6 of the mass and heattransfer surfaces 18.

[0042] The liquid distributor 20 is plugged onto the respective reactordouble plate 2 with a plug and socket connection 44. The cross sectionof the plug and socket connection 44 resembles the letter “M”, asdisplayed in FIGS. 5a, 5 b and 5 c. It is equipped with a centreplugging strip 46, which protrudes out of the bottom and left, right, inthe front and the rear a front cover strip 48 and a rear cover strip 50.The front cover strip 48 overlaps the first main surface 8 and the rearcover strip 50 overlaps the second main surface 10.

[0043] FIGS. 6 und 7 show a cross section of alternative designs of theliquid distributor 20. The designs in accordance with FIGS. 6 und 7 aredifferent from the design in accordance with FIG. 5 with regard to theshape of the liquid outlet openings 30 and 32. The front and rear liquidoutlet openings 30 and 32 are at the same level and are not staggeredsideways, as in the design in accordance with FIG. 5. In the design inaccordance with FIG. 6 the liquid supply sub-mains are directlyconnected with the liquid supply openings 30 and 32 and lead diagonallyoutwards and upwards to the top. In the design in accordance with FIG. 7these last liquid supply sub-mains 38 lead horizontally outwards. In thedesign in accordance with FIG. 7 the bifurcation 40 is rounded off toprevent turbulence and irregularities in the flow speed.

[0044]FIG. 8 shows a detail of FIG. 3 with rounded bifurcations 40. Atthe bifurcations 40 the liquid supply sub-mains are provided with awedge-shaped bulge, which complements the rounded form of thebifurcation.

[0045] To prevent the clogging of the smallest liquid supply sub-mains,the minimum cross section of the liquid supply sub-mains 38 is designedto be twice the size of the largest expected dust particle (typically 1mm²).

[0046] The ultra low flow liquid distributor as described above isparticularly suitable for use in a mass and heat transfer reactor forthe dehumidification and cooling of air. The air is dehumidified bymeans of a sorbent while at the same time the absorbing liquid, usuallya watery salt solution containing one or several salts, is considerablydiluted (absorption). Alternatively the air is humidified and thesorbens re-concentrated (Desorption). The heating and cooling liquid,which circulates in the heat transfer duct system 14 separated from theliquid sorbent FM and the air GM, transfers heat into or out of thesorption process (Desorption or Absorption). To achieve the maximumpossible cooling water temperature difference for absorption the coolingwater HKM is ducted in counter-flow or cross-counter-flow direction tothe airflow. For desorption it is ducted counter flow or cross-counterflow direction to the sorbent (FM). For absorption the most concentratedsorbent will be cooled the most, which keeps the vapour pressureequilibrium for the sorbent as low as possible. For the desorption themost concentrated sorbent is brought in contact with the hottest heatmedium HKM, which causes the highest possible increase in vapourpressure equilibrium in the sorbent. Both measures provide the greatestpossible mass transfer potential for the respective process (Absorptionor Desorption).

[0047] The mass and heat transfer surfaces 18, which separate thesorbent FM and the air GM from the cooling and heating agent HKM, at thevoid 12 between the reactor double plates 2 are in complete contact withthe heating and cooling media HKM and the other side, i.e. the mass andheat transfer surfaces 18 are moistened with the liquid sorbent FM. Theliquid sorbent FM forms an extremely thin, continuous film 26 on themass and heat transfer surfaces 18, which flows down the mass and heattransfer surfaces 18, following gravity. Due to the pure contact withliquids, on the inner side as well as on the outer side of the reactordouble plates 2, a high heat transfer coefficient and consequently ahigh heat transfer rate is achieved regarding the heat transfer from theheating and cooling liquid HKM through the separating wall into thesorbent FM and to the air GM, which flows along the thin film of sorbent26. This also ensures an optimal mass transfer. The continuous sorbentfilm 26 is achieved by use of a special coating 21 consisting of smallsolid particles 22, which enables an extremely small amount of sorbentto form a continuous moist surface on the mass and heat transfersurfaces 18 and which runs continuously to the bottom. The extremelysmall amount of sorbent is distributed by the liquid distributor 20across the upper edge of the mass and heat transfer surfaces 18 over theentire width of the reactor double plate 2, without forming droplets,which could be carried out by the airflow. The liquid distributor 20does not or only minimally protrude into the free cross section for theairflow between the reactor double plates 2, so that no significantdisturbance of the airflow occurs, which would lead to an increasedpressure loss.

[0048] The entire the mass and heat transfer reactor can be manufacturedin plastic (Polymers) and can be designed very thin. The thickness ofthe individual reactor double plates 2 for example is 3mm. In the void12 between the reactor double plates 2 fins (not shown) are inserted atregular intervals, so that the cooling liquid HKM flows through in theform of a meander. In the mass transfer duct system 16, which is formedbetween the reactor double plates 2, air GM flows against gravity whileliquid sorbent FM flows with gravity, forming a direct, continuouscounter flow.

[0049] Legend:

[0050]2 Reactor double plate

[0051]4 upper end of 2

[0052]6 lower end of 2

[0053]8 first main surface of 2

[0054]10 second main surface of 2

[0055]12 void between 2

[0056]14 heat transfer duct system

[0057]16 mass transfer duct system

[0058]18 mass and heat transfer surfaces

[0059]20 liquid distributor

[0060]21 coating of 18, 2

[0061]22 small solid particles, sand grains

[0062]24 gaps and voids

[0063]26 liquid film of sorbent FM

[0064]27 base body of 20

[0065]28 front side

[0066]29 rear side

[0067]30 front liquid outlet openings

[0068]32 rear liquid outlet openings

[0069]34 liquid supply system

[0070]36 liquid supply mains

[0071]38 liquid supply sub-mains

[0072]40 bifurcation

[0073]42 connection pipe of 36

[0074]44 Plug and socket connection

[0075]46 centre plugging strip

[0076]48 front cover strip

[0077]50 rear cover strip

[0078]52 wedge-shaped bulge

1.-11. (Canceled).
 12. An ultra low flow liquid distributor for minimumamounts of liquids for generating a thin liquid film on a transfersurface, said transfer surface providing direct contact between gas in agas volume and the liquid in said thin liquid film, said ultra low flowliquid distributor comprising: preferably an even number of liquidoutlet openings into said gas volume which are arranged along saidtransfer surface, which is to be moistened, a liquid supply systemstarting from a common main supply, which is branched by repetitivebisection at bifurcations into a multitude of liquid supply sub-mains,until each liquid supply sub-main feeds into one of said liquid outletopenings, wherein said liquid supply sub-mains are arranged below theliquid outlet openings.
 13. The ultra low flow liquid distributor inaccordance with claim 12, wherein said outlet openings are spaced atequal intervals.
 14. The ultra low flow liquid distributor in accordancewith claim 12, wherein said liquid supply sub-mains are arranged solelyin such a way that the liquid flow is flowing against gravity from thebottom to the top or across, perpendicular to gravity.
 15. The ultra lowflow liquid distributor in accordance with claim 12, wherein the crosssections of said liquid supply sub-mains is halved at each bifurcation,and the total length of each individual liquid supply sub-main from themain liquid supply to the respective liquid outlet opening is equal. 16.The ultra low flow liquid distributor in accordance claim 12, whereinsaid liquid supply sub-mains are of a rounded shape at the bifurcations.17. The ultra low flow liquid distributor in accordance with claim 12,comprising an attachment device for attaching the ultra low flow liquiddistributor at the transfer surface.
 18. The ultra low flow liquiddistributor in accordance with claim 12, comprising a base body in shapeof a panel with a front side and a rear side, wherein the liquid outletopenings are arranged in the upper section of the panel shaped basebody.
 19. The ultra low flow liquid distributor in accordance with claim18, wherein immediately neighboring liquid outlet openings arealternately fed to the front side and to the rear side.
 20. The ultralow flow liquid distributor in accordance with claim 12, wherein saidliquid outlet openings are arranged in a straight line.
 21. The ultralow flow liquid distributor in accordance with claim 12, wherein theliquid outlet openings are shaped conically, opening outwards.
 22. Amass and heat transfer reactor, comprising: two duct systems, which areisolated from each other with regard to the mass flow, but are coupledwith regard to the heat transfer, whereby there is a flow of a liquid orgaseous heating or cooling media in one duct system and in the otherduct system a flow of a gaseous media and a further liquid media; atleast one mainly vertically arranged reactor double plate with one upperend and one lower end, a primary and a secondary main surface and ahollow section between primary and secondary main surface; wherein theheat transfer duct system is accommodated in the void, at least one ofthe main surfaces is designed to serve as mass and heat transfersurface, said at least one mass and heat transfer surface is coated witha material to reduce the surface tension and/or has a surface structurewhich reduces the surface tension, at said mass and heat transfersurface the gaseous media and the liquid media are ducted in such a wayas to establish a counter flow, at the upper end of said at least onereactor double plate, a liquid distribution system is connected in sucha way as to establish a thin film of moisture of the liquid media onsaid at least one mass and heat transfer surface, and said liquiddistribution system is an ultra low flow liquid distributor inaccordance with claim
 12. 23. The ultra low flow liquid distributor inaccordance with claim 12, wherein each of said bifurcations comprises awedge-shaped bulge being symmetrically arranged with respect to thefluid streaming through each of said bifurcations.